Wave guide with electrical end termination



June 19, 1951 h J RADQ 2,557,686

WAVE GUIDE WITH ELECTRICAL END TERMINATION Filed March 27, 1946INVENTOR. JOHN A. RADO,

Patented June 19, 1951 UNITED STATES TENT OFFICE WAVE GUIDE WITHELECTRICAL END TEREHNATION Application March 27, 1946, Serial No.657,397

8 Claims.

This invention relates to wave guides including improved arrangementsfor delimiting their electrical lengths.

As used broadly in this specification and in the appended claims, theterm wave guide applies to a system of conductive surfaces which act asthe boundaries of an electric wave and have the ability of directing thepropagation of such a wave, much as the rigid walls of a speaking tubeguide sound by preventing the sound from spreading freely into space.Wave guides are well known in the art and may take the form of two ormore separated conductors in open space, such as a power line or atelephone line. This type may be called transmission lines of theopen-wire line variety. Another type of wave guide comprises simply asingle hollow conductor capable of propagating the wave through itsinterior; this type may be called a hollow guide. Still other typesinclude one or more conductors enclosed within but electricallyinsulated from another conductor, as in the conventional coaxial line.While certain details of design and method of excitation may depend onthe type of guide and manner of its use, the term wave guide is usedhere in its generic sense, including any of the types mentioned, andrefers also to the relatively short guides often designated as cavityresonators.

A prior arrangement used to determine the effective length of a Waveguide is a simple shortcircuiting bar or end cap which reflects currentsflowing in the guide structure. When the guide is so disposed andexcited as to operate in a resonant condition, high currents may flowbetween such a short-circuiting device and the adjacent portion of theconductive surfaces of the guide. This high current condition introducestroublesome contact problems, especially when the shorting device mustbe movable along the guide to adjust its length over a range of Values.

Another prior device, used in the types of Wave guides having a hollowcylindrical conductor, comprises a piston-like structure or tuner closedat one end and having a length approximately equal to one-quarter of theoperating wave length. Such a piston functions in effect as aquarter-wave end section of the guide and, if r desired, may be movableto produce variations in the electrical length. With this arrangement,contact between the piston and the active part of the guide may be madeat points far enough away from the point of current maximum that thecurrents flowing at the points of contact are appreciably smaller thanis the case with a simple shorting device. While this arrangementdecreases the deleterious elfects of high or variable contactresistances, experience has shown that some effect remains and maybecome objectionable in certain applications.

A so-called choke arrangement also has been used to determine theelectrical length of a tubular wave guide. In this arrangement a plugfits inside the tubular guide, but is spaced therefrom to provide achannel. If this channel is made of a proper resonant length, the guidemay be effectively terminated at the face of the plug. This arrangementdiffers from. the piston-like structure mentioned above in that the plugdoes not function as an end section of the guide, the face only of theplug delimiting the electrical length of the guide. When such a plug isused,

the over-all guide structure must have an extra length, necessary toobtain the proper resonant condition in the channel between the plug andthe inner wall of the guide structure. Also, with a choke-plugarrangement the deleterious efiects of high or variable contactresistance still may be experienced. Here a contact is establishedbetween the inner wall of the guide structure and the supporting elementof the plug.

It is an object of this invention, therefore, to provide an arrangementwhich substantially avoids one or more of the above-mentionedlimitations of the described prior arrangements.

It is a further object of this invention to provide a wave guide havingan improved arrangement for determining its electrical length.

A more specific object of the invention is to provide a wave guide ofadjustable electrical length having improved efiiciency and increasedfreedom from deleterious effects due to contact resistance.

A still further object is to provide an improved means for supporting ashort-circuited pistontype tuner in a wave guide.

In accordance with the invention, a wave guide comprises a conductivestructure including at least one longitudinally extending conductivesurface defining a wave-propagating space for guiding electromagneticwaves. A short-circuited guide section, having an effective electricallength equal to an odd integral multiple of one-quarter wave length atthe operating frequency of the guide, is longitudinally disposed withinthis propagating space to determine the electrical length of the waveguide. The short-circuited section includes at least one conductiveportion adjacent to but spaced from the conductive surface of the guidestructure and provides therewith an open-circuited transmission-linesection having an electrical length of an odd number of quarter- Wavelengths at the operating frequency. The wave guide also includes meansfor supporting the open end of the short-circuited section withreference to the last-mentioned conductive surface of the structurecomprising a dielectric 3 member positioned within the transmission-linesection adjacent the open end of the short-circuited section.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

In the drawing, Fig. 1 is an axial section through one end portion of awave guide of the coaxial transmission-line type embodyin the presentinvention; Fig. 2 is a transverse section through the wave guide of Fig.1; Fig. 3 is an axial section through one end portion of a hollow guideembodying the invention; Fig. 4 is a plan view of one end portion of awave guide of the open-Wire transmission-line type embodying theinvention; and Fig. 5 is a sectional elevation of the wave guide of Fig.4.

Referring to Figs. 1 and 2 of the drawing, there is shown an end portionof a wave guide comprising a conductive structure including a pluralityof longitudinally extending conductive surfaces on portions Ii], IIdefining a wavepropagating space I2 for guiding electromagnetic waves.The conductive structure shown is of the coaxial type in which theconductive portion or surface I8 is a hollow cylindrical outer conductorand the conductive portion II is a coaxially aligned hollow innerconductor, establishing the wave-propagatin space I2 between the outerand. inner conductors as in conventional coaxial lines. An end plate I3aligns and spaces the conductors I and II.

A short-circuited guide section I5, also of the coaxial type, isprovided. The section I is disposed within and longitudinally adjustablealong the wave-propagating space, in the embodiment illustrated, inorder to effect tuning of the guide over a range of operatingfrequencies. The section includes longitudinally extending conductiveportions shown as two hollow cylindrical conductors I6 and H, the innerconductor I1 and outer conductor I6 being coaxially aligned. Theseconductors are conductively connected at one end by a short-circuitingdiaphragm I8 and, in the usual construction, are selected of such lengththat the section I5 has an effective electrical length approximatelyequal to one-quarter wave length at the mean operating frequency of theguide structure.

At least one, but preferably both, of the conductors of section I5 areadjacent to but spaced from the corresponding conductors of the guidestructure and provide therewith open-circuited transmission-linesections, individually having an approximate electrical length ofone-quarter wave length at the mean operatin frequency. Thus, in theillustrated embodiment, the inner conductors II and I! have a separation29 and constitute a quarter-wave line section that is open-circuited ateach end. Similarly, the outer conductors II) and I6 have a spacing 22and form an open-circuited line section of the same length.

An adjustable short-circuiting section of the type illustrated may beconveniently referred to as a tuning piston or cup that is closed at oneend by diaphragm I8 and is open at the opposite end. A means is providedfor supporting the open end of piston I 5 with reference to innerconductor I l of the guide structure. This means comprises a dielectricmember or ring 25, positioned within the space 20 between conductors IIand I1 and, therefore, positioned within the transmission-line sectionformed by those conductors. Ring 25 further i positioned adjacent theopen end of piston I5, and is constrained for movement with the pistonby a suitably shaped recess 24 formed by a rib integral with the freeend of conductor I! and thus near the open end of the piston. A materialmolded of, or impregnated with, a phenolic resin is suitable for ring25. For purposes of assembly, the ring may be segmented and the segmentsseparately fitted into the recess, or the recess may be formed bycrimping the free end of conductor I! over a continuous dielectric ring.

A support 21 of generally toroidal shape is located behind the closedend of piston I5 to support that end in coaxial alignment withconductors I0 and II. Support 2'! is preferably of insulating material,and may be of a phenolic material havin high dielectric-loss propertiessince it is outside of the active propagatin space and need havemechanical strength sufficient to support only one end of piston I5. Thesupport 27 is fastened to short-circuiting diaphragm I8 by means ofelements such as screws 34.

Piston I5 and its support 21 are longitudinally adjustable through adriving mechanism including a driving rin 28 positioned within conductorII. Slots 29, 30 are out into conductor II and extend longitudinally fora distance somewhat greater than the desired traverse of piston I5during adjustments of the guide structure. Keying pins 3|, 32 passthrough slots 29, 30 and connect driving ring 28 with support 21. Ring28 has an internal thread for engaging externally driven lead screw 33.The screw has suitable shoulders bearing against end plate I3 to preventlongitudinal movement. Suitable means (not shown), including acalibrated tuning dial, may be provided for rotating lead screw 33 toeffect and indicate a longitudinal displacement of driving ring 28within conductor I I and a corresponding displacement of piston I5within the wave-propagatin space I2. If sup port 21 is of an insulatingmaterial, the entire piston can be placed at a direct current voltage orlow-frequency (power-supply) voltage different from the voltage of therest of the guide structure. The short-circuiting member, supportedaccording to the invention, may be used to determine a fixed electricallength, in which case the support 21 may be afiixed to the guideconductors and the lead screw omitted.

If, in operation of the wave guide of Figs. 1 and 2, it is desired totune over a range of operating frequencies, longitudinal adjustments ofthe piston are made by rotating lead screw 33.- During the adjustment,dielectric ring 25 slides along inner conductor II, and the position ofthe short-circuited end of the piston, relative to the remote end (notshown) of the guide structure, determines an adjustable active length ofthe guide. Accordingly, the effective electrical length of the guide isdelimited by the diaphragm I8 of the piston I5. During resonantoperation, current is reflected at the closed end of the piston, and thereflected wave energy combines with wave energy traveling toward thepiston to produce alternate points of low and high peak current spacedalong the guide at intervals of onequarter wave length. Thus, standingwaves are produced in a well-known manner, with maximum current atshort-circuiting diaphragm i8 and minimum current at the open end of thequarter-wave piston. The physical length of the piston corresponding toan electrical length equal to a quarter-wave length is not extremelycritical, and it is usually entirely satisfactory to proportion theparts as if for operation at some frequency Within the desired range,approximately the mean frequency.

To obtain effective electrical connection between the conductors of theguide and a shortcircuited guide section of the specified length, it isnot necessary that every portion of those conductors have acorresponding adjacent portion in the short-circuited section. Moreover,when the short-circuited section includes conductive portions adjacentto but spaced from a substantial portion of the conductive surfaces ofthe re- 1 mainder of the wave guide, there ordinarily is sufiicientcoupling between those portions of the short-circuited section and therest of the structure to ensure effective electrical connection at radiofrequencies by means of that coupling alone. Under these conditions, nophysical contact is necessary at any point between the shortcircuitedsection and the rest of the guide. Thus, the short circuit isefiectively provided without any deleterious eiiects due to the variableresistance of contacts between the short-circuiting member and theconductive structure of the wave guide.

Regarding the location of dielectric ring 25, it may be noted that powerloss in a dielectric material not only depends on the loss properties ofthe dielectric, but also is proportional to the square of the voltagegradient in the dielectric. At the open end of piston l5, efiectivecontact is made between the piston and the conductors It] and II where acondition of low peak current but high peak voltage exists in thewave-propagating space. If the open end of the guide section were to besupported by a dielectric member within the Wave-propagating space atthis high volt-age point, that member would have to be of an expensivematerial having low dielectric-loss properties, such as one of thebetter electrical grades of a polystyrene or polyethylene material, oran inorganic composition such as fused quartz or a steatite materialmade especially for highfrequency radio applications. Suitability of agiven material often depends, of course, on the operating frequenciesinvolved. If used in this manner, any materials exhibiting dielectriclosses substantially higher than those of the named materials wouldimpair seriously the operation of the wave guide. In accordance with theinvention, however, ring 25 is located within the transmission-linesection 26 provided by conductors H and H, to avoid such limitations.

Any wave energy which may enter the trans mission-line section 20 fromthe propagating space !2 of the guide travels to the far end of thesection adjacent the short-circuiting diaphragm it. This far end ofsection 2!! is opencircuited, and is a point of voltage reflection whereno current can flow. Consequently, wave energy traveling down thetransmission-line section is reflected at the far end and sets upstanding waves within the transmission-line section itself with a pointof voltage maximum at its far end and (considering the transmission-linesection alone) a point of voltage minimum and current maximum aquarter-wave length along the line section from its far end. Since theline section has a length of one-quarter of the operating wave length,its near end represents a point of voltage minimum. The supporting ring25 is positioned within line section 26 adjacent its near end so that noappreciable voltage gradient exists in the space in which the ring 25 ispositioned. By so positioning the ring, it is effectively protected fromthe high-voltage field in the wavepropagating space l2 of the guide,shielding the ring from the fields established in the guide. Positioningthe ring in recess 24 augments the shielding.

A dielectric member so positioned in a region of low-voltage gradientmay be made of a relatively inexpensive material having relatively highdielectric-loss properties without seriously increasing the powerlosses. Materials having such properties and also suitable mechanicalproperties include cellulose acetate, resins of the phenolformaldehydeand polymethyl methacrylate types, and certain cross-linked additionpolymers identified as allyl resins.

Even using a relatively high-loss material for dielectric member, thewave guide of the invention operates with high efficiency. Moreover, theconstruction is such as to provide high mechanical strength andrigidity, which may be necessary under conditions of severe vibration.It is notable further that the transmission-line section Ell not onlyhas low voltage across it at the point adjacent the open end of thepiston, but also (considering the wave guide as a whole) has low currentat that point, since it is at a point of low current in thewave-propagating space l2. Since neither appreciable voltage nor currentexists across the section 2!! at the point where it opens into thewave-propagating space 12, very little power is applied to the sectionby the energy in that space. The transmission-line section 29 is thusonly weakly excited. It is apparent that this is also true of the linesection 22. It follows that there can be very little leakage of energyfrom the wave guide at the point where it is terminated by theshort-circuited guide section. Since there may nevertheless be somevoltage field at the far ends of these transmission-line sections, itmay prove desirable to cut away portions of the support 2?, as shown, sothat it touches member It only at the central portion of the member.Such a construction substantially shields this support from the fieldsestablished in the guide structure.

Fig. 3 shows the application of the invention to a hollow wave guideincluding a conductive surface comprising at least two portions 48 andM. These portions comprise opposing surfaces of a hollow conductivestructure defining a wavepropagating space 42. The hollow structure isprovided with an end plate 63, and may have any of the variouscross-sectional shapes known to the art as suitable for hollow guides.

A short-circuited section is longitudinally disposed within propagatingspace G2 to determine the electrical length of the guide. The section 55includes conductive portions 45 and 57, comprising opposing surfaces ofa hollow section preferably similar in cross section to the hollowconductive structure, and situated adjacent to but spaced from thecorresponding wall portions to and ti, respectively, of the hollowstructure. Section 35 thus provides with the walls of the hollowstructure a transmissionline section 58 open-circuited at each end. Theshort-circuited section &5 has the form of a tuning piston or cup closedat one end by short circuiting disc at. The conductors ii; and ii areselected of such length that piston 35 and transmission-line section sohave effective electrical lengths equal to an odd integral multiple ofonequarter wave length at the operating frequency of the guide, usuallyone-quarter wave length, as with the coaxial line of Figs. 1 and 2.

Referring again to Fig. 3, a recess formed by an integral rib A, nearthe open end of piston 45, positions a dielectric member 55 withintransmission-line section 56 for supporting the open end of the pistonwith reference to the walls of the hollow structure. In the embodimentillustrated, the piston 45 is longitudinally adjustable for tuning theguide, and the recess 54 may be formed in any manner suitable toconstrain member 55 for movement with the piston. As in the embodimentillustrated in Figs. 1 and 2, the dielectric member 55 may extendcontinuously around the piston, or may comprise a number ofcircumferential segments capable of being slipped into recess 54 beforethe piston is inserted into the hollow structure. A continuousdielectric ringadvantageously may be used on a cylindrical piston, whilethe segmented type of dielectric member is applicable particularly toguide structures of rectangular cross section.

An insulator 5'! is aflixed behind the closed end of piston 25. A leadscrew 58 is held rotatably captive within a bushing portion of insulator5?. Screw 58 passes through a tapped bushing 59 afiixed to end plate 43.Rotation of the lead screw by appropriate means (not shown) causesinsulator 57 and dielectric member 55 to slide along the hollowstructure Ml, ti, and accomplishes longitudinal tuning adjustments ofpiston 45 along the propagating space 52.

In spite of certain differences in their exact electrical behavior, theparts of the hollow guide of Fig. 3 embodying the present inventionoperate in a manner similar to the operation of the coaxial line ofFigs. 1 and 2.

Figs. 4 and 5 illustrate the invention as applied to a wave guide of theopen-wire line type. The wave guide comprises a pair of spacedlongitudinally extending conductors S3 and 66 defining awave-propagating space 62. A spreader 63 aligns and spaces theconductors Eli and 6! at the end portion of the wave guide illustrated.

A short-circuited section 65 is longitudinally disposed within thepropagating space 62 to determine the electrical length of the guide.The section 65 includes conductive portions 66 and 61, adjacent to butspaced from substantial portions of the conductors 60 and 6!,respectively. Thus, conductors 6E} and 66 have a separation 10,providing an open-circuited transmission-line section. An identicaltransmission-line section II is provided by conductors GI and 61. Ashort-circuiting bar 68 is conductively connected to the conductors 66and 61 of the section. Dielectric ring segments '15 and are positionedwithin the transmission-line sections 19 and H, respectively,'adjacentthe open end of short-circuited section 65 to furnish support withreference to the conductors 60 and SI. The segments 15 and 16 areconstrained near the open end of section 65 by expansions 13 and 14forming recesses in the conductive portions 66 and 51. The segments areforced to bear against the conductors 60, 6| by connecting theconductors 66, 61 to the short-circuiting bar 68 in such a manner as toprovide spring action forcing the conductors 66, 61 apart at the openend of section 65.

To align the short-circuited end of the section, a support 11 isfastened to short-circuiting bar 68 by screws 84. The other end ofsupport 11 is fastened to a centering insulator I8, which has two holesthrough which the spaced conductors B0 and BI pass. The conductors 66and. 61 of the section 65 are chosen of suitable resonant lengths, aswith the other embodiments of the invention described above. Theinsulator 18 may be moved longitudinally of the guide to effect tuningadjustments of the piston, operation of the openwire line being quitesimilar to operation of the coaxial line of Figs. 1 and 2.

While there have been described what are at present considered to be thepreferred embodi ments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

l. A wave guide comprising, a conductive struc ture including at leastone longitudinally extending conductive surface, said structure defininga wave-propagating space for guiding electromagnetic waves, ashort-circuited guide section having an effective electrical lengthequal to an odd integral multiple of one-quarter wave length at theoperating frequency of said guide and longitudinally disposed Withinsaid propagating space to determine the electrical length of the waveguide, said short-circuited section including at least one conductiveportion adjacent to but spaced from said conductive surface of saidstructure and providing therewith an open-circuited transmission-linesection having an electrical length of an odd number of said quarterwave lengths, and means for supporting the open end of saidshort-circuited section with reference to said conductive surface ofsaid structure comprising a dielectric ring positioned within saidtransmission-line section adjacent said open end.

2. A wave guide comprising, a conductive structure including at leastone longitudinally extending conductive surface, said structure defininga wave-propagatin space for guiding electromagnetic waves, ashort-circuited guide section having an effective electrical lengthequal to an odd integral multiple of one-quarter wave length at theoperating frequency of said guide and longitudinally disposed withinsaid propagating space to determine the electrical length of the waveguide, said short-circuited section including at least one conductiveportion adjacent to but spaced from said conductive surface of saidstructure and providing therewith an open-circuited transmission-linesection having an electrical length of an odd number of said quarterwave lengths, and means for supporting the open end of saidshort-circuited section with reference to said conductive surface ofsaid structure comprising a dielectric ring having high dielectriclossproperties at said operating frequency and positioned within saidtransmission-line section adjacent said open end.

3. A wave guide comprising, a conductive structure including at leastone longitudinally extending conductive surface, said structure defininga wave-propagating space for guiding electro-magnetic waves, ashort-circuited guide section having an effective electrical lengthequal to an odd integral multiple of one-quarter wave length at theoperating frequency of said guide and longitudinally adjustable withinsaid propagating space to determine the electrical length of the waveguide, said short-circuited section including at least one conductiveportion adjacent to but spaced from said conductive surface of saidstructure and providing therewith an open-circuited transmission-linesection having an electrical length of an odd number of said quarterwave lengths, and means for supporting the open end of saidshort-circuited section with reference to said conductive surface ofsaid structure comprising a dielectric ring positioned within saidtransmission-line section adjacent said open end and constrained formovement with said shortcircuited section.

4. A wave guide comprising, a conductive structure including at leastone longitudinally extending conductive surface, said structure defininga wave-propagating space for guiding electromagnetic waves, ashort-circuited guide section having an effective electrical lengthequal to an odd integral multiple of one-quarter wave length at theoperating frequency of said guide and longitudinally adjustable withinsaid propagating space to determine the electrical length of the waveguide, said short-circuited section including at least one conductiveportion which has a recess near the open end of said guide section andis positioned adjacent to but spaced from said conductive surface ofsaid structure to provide therewith an open-circuited transmissionlinesection having an electrical length of an odd number of said quarterwave lengths, and means for supporting the open end of saidshort-circuited section with reference to said conductive surface ofsaid structure comprising a dielectric ring positioned within saidtransmission-line section adjacent said open end and constrained by saidrecess for movement with said short-circuited section.

5. A wave guide comprising, a longitudinally extending hollow conductivestructure defining a wave-propagating space for guiding electromagneticwaves, a short-circuited guide section having an effective electricallength equal to an odd integral multiple of one-quarter wave length atthe operating frequency of said guide and longitudinally disposed withinsaid propagating space to determine the electrical length of the waveguide, said short-circuited section including conductive portionsadjacent to but spaced from the walls of said hollow structure andproviding therewith an open-circuited transmissionline section having anelectrical length of an odd number of said quarter wave lengths, andmeans for supporting the open end of said short-circuited section withreference to said hollow conductive structure comprising a dielectricmember positioned within said transmission-line section adjacent saidopen end.

6. A wave guide comprising, a pair of spaced longitudinally extendingconductors defining a wave-propagating space for guiding electromagneticwaves, a short-circuited guide section having an effective electricallength equal to an odd integral multiple of one-quarter wave length atthe operating frequency of said guide and longitudinally disposed withinsaid propagating space to determine the electrical length of the waveguide, said short-circuited section including at least one conductiveportion adjacent to but spaced from one of said conductors and providingtherewith an open-circuited transmissionline section having anelectrical length of an odd number of said quarter wave lengths, andmeans for supporting the open end of said short-circuited section withreference to said one conductor comprising a dielectric ring positionedwithin said transmission-line section adjacent said open end.

7. A wave guide comprising, a conductive structure of the coaxial typeincluding a hollow cylindrical outer conductor and a coaxially alignedinner conductor defining a wave-propagating space for guidingelectromagnetic waves, a shortcircuited guide section of the coaxialtype including hollow coaxially aligned inner and outer conductorshaving an effective electrical length equal to an odd integral multipleof one-quarter wave length at the operating frequency of said guide andbeing longitudinally adjustable within said propagating space todetermine the electrical length of the wave guide, said inner conductorof said short-circuited section having a recess near the open end 'ofsaid section and being adjacent to but spaced from said inner conductorof said conductive structure to provide therewith an open-circuitedtransmissionline section having an electrical length of an odd number ofsaid quarter wave lengths, and means for supporting the open end of saidshort-circuited section with reference to said inner conductor of saidconductive structure comprising a dielectric ring positioned within saidtransmission-line section adjacent said open end and constrained by saidrecess for movement with said short-circuited section.

8. A wave guide comprising, a conductive structure of the coaxial typeincluding a hollow cylindrical outer conductor and a coaxially alignedinner conductor defining a wave-propagating space for guidingelectromagneticwaves, a shortcircuited guide section of the coaxial typeincluding hollow coaxially aligned inner and outer conductors having aneffective electrical length equal to an odd integral multiple ofone-quarter wave length at the operating frequency of said guide andbeing longitudinally adjustable within said propagating space todetermine the electrical length of the wave guide, said inner conductorof said short-circuited section having a recess near the open end ofsaid section and being adjacent to but spaced from said inner conductorof said conductive structure to provide therewith an open-circuitedtransmission-line section having an electrical length of an odd numberof said quarter wave lengths, and means for supporting the open end ofsaid short-circuited section with reference to said inner conductor ofsaid conductive structure comprising a ring having high dielectric-lossproperties at said operating frequency positioned within saidtransmission-line section adjacent said open end and constrained by saidrecess for movement with said short-circuited section.

JOHN A. RADO.

REFERENCES CITED The following references are of record in the file ofthis patent:

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